A holographic recording and reproducing apparatus using a transmissive recording medium is known as an apparatus utilizing holography. For example, U.S. Pat. Nos. 7,092,133 B2 and 7,167,286 B2 disclose examples of holographic apparatuses using the transmissive recording medium.
Referring to FIG. 18, an example of the holographic apparatus using the transmissive recording medium has a light source 101, a spatial laser modulator (SLM) 102, CCD camera 103, objective lens 104, polarizing beam splitters (PBS) 105a, 105b, 105c and mirrors 106a-106i. The SLM adds recording data to an emitted laser beam from source 101. CCD camera 103 reads reproducing light from a recording medium 107. A recording layer of recording medium 107 is set at a focus position of objective lens 104.
Regarding the holographic apparatus using the transmissive recording medium, a recording process will be described in FIG. 19 hereinafter.
Referring to FIG. 19, PBS 105a divides a laser beam emitted from light source 101 into two laser beams which are an information light beam and a reference light beam. The information light travels towards PBS 105b, and the reference light travels toward PBS 105c. 
The information light penetrates PBS 105b, traveling towards SLM 102. SLM 102 adds the recording data to the information light. The information light enters PBS 105b again, being reflected by PBS 105b, traveling towards objective lens 104, and being focused on recording medium 107.
On the other hand, the reference light is reflected by PBS 105c, traveling toward mirrors 106a, 106b, 106c and 106d, and traveling toward recording medium 107. When the reference light enters mirrors 106b, the incident angle at recording medium 107 varies by changing the angle of mirrors 106b. 
Accordingly, it is possible for the incident angle with the information light focused on objective lens 104 to be changed. Consequently, since interference pattern provided in recording medium 107 can be changed, multiple recording can be performed.
Now, the reproducing process will be described with reference to FIG. 20.
Referring to FIG. 20, light source 101 radiates a laser beam as a reference light. The laser beam penetrates PBSs 105a and 105c, traveling toward mirror 106e. Mirrors 106e, 106f, 106g, 106h and 106i lead the laser beam to recording medium 107. When the laser beam enters recording medium 107, the incident angle can be changed by mirror 106g. 
When the reference light penetrates the interference pattern recorded on recording medium 107, the recording data is reproduced as reproducing light. The reproducing light penetrates objective lens 104 and PBS 105b, and is read by CCD camera 103. CCD camera 103 reproduces the recording data.
However, since a recording medium that incident laser beam penetrates is used for the above-mentioned hologram apparatus, the reproducing light is emitted on the opposite side to the incident side of the reference light during the reproducing process. An optical system is required to be located at both sides of the recording medium in order to reproduce the holographic recording data.
Therefore, since it is necessary to dispose the optical system at both sides of the recording medium, the number of parts for the recording and reproducing processes increases. Accordingly, it is difficult to downsize the hologram apparatus using the transmissive recording medium.
A holographic recording and reproducing apparatus using a reflective recording medium is known as a downsized hologram apparatus.
Referring to FIG. 21, an example of the holographic apparatus using the reflective recording medium has light source 101, SLM 102, CCD camera 103, objective lens 104 and PBSs 108a, 108b and 108c. The recording layer of recording medium 107 is disposed at a focus position of objective lens 104.
Regarding the holographic apparatus using the reflective recording medium, a recording process will be described with reference to FIG. 22.
Referring to FIG. 22, PBS 108a splits a laser beam emitted from light source 101 into two laser beams. The laser beam traveling toward SLM 102 is referred to as “information light,” and the laser beam traveling toward PBS 108c is referred to as “reference light.”
PBS 108a reflects the information light. SLM 102 adds recording data to the information light. The information light travels toward PBS 108b. When PBS 108b reflects the information light, it travels toward objective lens 104. Finally, the information light is focused on recording medium 107.
On the other hand, the reference light is reflected by PBS 108c, being focused through PBS 108c on recording medium 107 by objective lens 104.
Next, the reproducing process will be described with reference to FIG. 23.
The laser beam emitted from light source 101 is used as the reference light. The reference light travels toward objective lens 104 through PBSs 108a, 108b and 108c. 
When an interference pattern provided in recording medium 107 diffracts the reference light, reproducing light indicating the recording data is generated. CCD camera 103 receives the reproducing light through objective lens 104 and PBSs 108b and 108c, reads out the recording data from the reproducing light, and reproduces the read recording data.
However, the holographic apparatus using the reflective recording medium maintain a constant position at which the information light and the reference light are focused in the thickness direction of the recording medium. Accordingly, since the interference area is constant, it is difficult to perform multiple recording using the reflective recording medium. Although a shifted multiple scheme is known as holographic method performing multiple recording, it has been desired to appear the holographic apparatus using the reflective recording medium and performing multiple recording.